The present invention relates to a method of and an apparatus for cleaning an oil-deposited material, as well as a cleaning agent used therefor, and more in particular, it relates to a method of and an apparatus for cleaning an oil-deposited material for effectively cleaning and removing oils deposited (extraneous oils) to a material to be cleaned such as metal parts, as well as a cleaning agent used therefor.
In a step of cutting fabrication for metal parts such as precision instrument parts and electric parts, cutting oils, etc. are used with an aim of reducing friction between a material to be cutting-worked and a cutting tool, removing a great amount of frictional heat generated upon fabrication, washing out of cutting wastes, improving the working life of cutting tools and smoothing a finished surface.
Accordingly, oils are deposited to a fabricated metal material and the fabricated metal material can not be used as a final product as it stands in a state where the oils are deposited. Accordingly, in a finishing step for such parts, oils are cleaned and removed by using organic solvents.
As known organic solvents used for cleaning and removing the oils, hydrocarbon-type solvents such as kerosene, benzene and xylene, chloro-type solvents such as trichloroethylene and tetrachloroethylene and flon-type solvents such as trichlorofluoroethane, etc. can be used. In particular, flon- or chloro-type solvents having high cleaning ability and incombustibility have been used for cleaning electronic, electric, or machinery metal parts.
However, among the known organic solvents described above, the hydrocarbon solvents, in particular, benzene and xylene are compounds having high toxicity and specified as deleterious materials in view of labor safety law, and accordingly, there has been a problem of risk and trouble for a handling operation. Further, the chloro- or flon-type solvents involve a great problem, for example, in view of safety, toxicity and environmental pollution.
For overcoming the foregoing problems in cleaning agents comprising organic solvents such as benzene and xylene, and flon-type solvent, the following cleaning agents have been proposed.
Japanese Patent Application Laid-Open (KOKAI) No. 49-128908 proposes a cleaning agent composition containing N-methyl-2-pyrrolidone and a surfactant, in which the content of the surfactant is 0.1 to 30% by weight based on the sum of both components.
Japanese Patent Application Laid-Open (KOKAI) No. 1-188311 proposes a mold cleaning agent containing not less than 20% by weight of pyrrolidone and/or derivative thereof, and if necessary, a viscosity improver, a surfactant and a solvent such as monohydric alcohols, polyhydric alcohols (for example, ethylene glycol, diethylene glycol, propylene glycol, glycerine, cellosolves and carbitols), dimethylsulfoxide, diethylsulfoxide, N,N-dimethylformamide or N,N-dimethylacetamide.
Japanese Patent Application Laid-Open (KOKAI) No. 4-68094 proposes a degreasing and cleaning agent comprising, as the essential ingredient:
(1) a nonionic surfactant of 1 to 30% by weight, and PA1 (2) one or more of compounds selected from N-methylpyrrolidone, 2-pyrrolidone, r-butyrolacton. dimethylsulfoxide, sulfolane and propylene carbonate.
However, the proposed cleaning agents still involve problems in view of safety, sanitation for working circumstance and environmental pollution.
As a result of the present inventors' earnest studies, it has been found that by cleaning a material having oils deposited on the surface thereof with a cleaning agent containing at least one of pyrrolidones, .gamma.-butyrolacton and N,N-dimethylacetamide, and water, eliminating at least a portion of the deposited cleaning agent from the material to be cleaned by a physical means, and then water-washing the material with water and/or steams, an oil-deposited material can be cleaned with an excellent degreasing and cleaning effect for oils, with a satisfactory safety and sanitation for working circumstance and with a less burden for waste-water treatment, and can be free from the worry of environmental contamination. The present invention has been attained on the basis of this finding.